Climate change profoundly affects the interannual variability (IAV) of net primary production (NPP) of terrestrial ecosystem from multiple aspects. However, the IAV of the nationwide annual NPP in China and the impacts of distinct climatic drivers are not well addressed. In this study, we investigated regional contributions to the IAV of the nationwide NPP and quantified the contributions of nine climatic drivers in different regions using the NPP estimated by the Carnegie-Ames-Stanford (CASA) model from 1982 to 2018. Our results showed that the simulated NPP exhibited an increasing trend of 15.2 Tg C yr^-1 at the national scale. The nationwide NPP also showed large IAV ranging from ‍-0.29 to 0.22 Pg C with the mean absolute NPP IAV showing a descending gradient from southeastern to northwestern China. Our estimates and thirteen terrestrial biosphere models verified that humid region accounted for the largest contribution (62%) to this large IAV. Attribution analyses indicated that normal and high precipitation amount (nP, HP), as well as high temperature days (HT) and daily temperature range (DTR) exerted the largest contributions to the national NPP IAV. Regional analyses indicated that DTR and HP were the major climatic drivers to NPP IAV in humid region, whereas NPP IAV in water-limited regions (i.e., semi-humid, semi-arid, and arid regions) were tightly associated with nP, HP, and HT. DTR and nP exerted the largest contributions to NPP IAV in the Tibetan Plateau. However, more attention should be paid to the negative impacts of low temperature events and potential drought on NPP IAV in humid region and that of HT in water-limited regions. This study emphasized the dominant role of humid region in controlling the national NPP IAV and the different ecosystem responses to diverse climatic drivers, and therefore can be valuable for adaptive management of ecosystems when facing climate change.